The present invention relates to semiconductor processing and, more particularly, to a system and method for monitoring characteristics of a rotating substrate.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these higher densities, efforts continue toward scaling down device dimensions (e.g., at sub-micron levels) on semiconductor wafers. To accomplish such high device packing densities, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The process of manufacturing semiconductors, or integrated circuits, typically consists of more than a hundred steps, during which numerous of copies of an integrated circuit may be formed on a single wafer. Generally, the process involves creating several patterned layers on and into the substrate that ultimately form the complete integrated circuit. Fabricating a semiconductor using such sophisticated manufacturing techniques may involve a series of steps including cleaning, thermal oxidation or deposition, masking, etching, and doping.
Wafers may be pre-cleaned using, for example, high-purity, low-particle chemicals. Silicon wafers may be heated and exposed to ultra-pure oxygen in diffusion furnaces under carefully controlled conditions to form a silicon dioxide film of uniform thickness on the surface of the wafer.
A masking step is utilized to protect one area of the wafer while working on another area. This process typically includes photolithography or photo-masking. A photoresist or light-sensitive film is applied to the wafer, such as while supported in a suitable spin coating apparatus. A photoaligner aligns the wafer to a mask and then projects an intense light through the mask and through a series of reducing lenses, exposing the photoresist with the mask pattern.
The wafer is then xe2x80x9cdevelopedxe2x80x9d (the exposed photoresist is removed), such as by applying a developing solution while rotating the substrate on a suitable support. The developed substrate may then be thermally baked to harden the remaining photoresist pattern. It is then exposed to a chemical solution or plasma (gas discharge) so that areas not covered by the hardened photoresist may be etched away. The photoresist is removed using additional chemicals or plasma. In order to ensure correct image transfer from the mask to the top layer, various wafer inspection methodologies may be employed.
Various process conditions affect formation of layers during semiconductor fabrication. Such conditions further can vary from batch to batch, which variations tend to cause inconsistencies in the resulting products. For example, a non-uniform film thickness can introduce overlay errors and other defects that can adversely affect a resulting integrated circuit formed on the substrate. Accordingly, measurement and inspection systems and techniques have been developed to analyze characteristics of a substrate in between different processing stages. However, when fatal defects are detected after a particular process has completed, structures having such defects typically have to be discarded.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides a system and method for monitoring characteristics of a substrate. The substrate is supported on a moveable support, such as adapted to rotate about an axis during part of a fabrication process. A measuring system is operable to emit an incident beam onto gratings and/or features of the substrate near the axis about which the substrate is rotating. The beam interacts with the substrate to produce a reflected and/or diffracted beam(s). The reflected and/or diffracted beam can be analyzed to determine substrate characteristics. In order to facilitate measuring feature characteristics, in accordance with an aspect of the present invention, the measuring system emits the incident beam as a function of the rotation of the moveable support such as to interrogate the gratings and/or features at a desired angle relative to the incident beam. As a result, the incident beam is able to selectively interrogate gratings and/or features on the substrate, thereby mitigating errors due to movement of the substrate.
Another aspect of the present invention provides a system for measuring characteristics of a substrate. The system includes a positioning system having a support for receiving a substrate and rotating about a rotational axis. A measurement system includes a light source. When the light source is activated, the light source emits light onto a central region of the substrate based on the angular orientation of the rotating substrate.
Another aspect of the present invention provides a method for measuring characteristics of a substrate. The substrate is rotated about an axis that extends through the substrate while supported within a processing environment. An incident light beam is emitted onto the substrate near the axis. The incident light beam is emitted based on the angular orientation of the substrate. As a result, the incident beam can selectively interrogate the substrate near the axis when the substrate is at a desired angular orientation relative to the incident beam.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.